Intervalometer and timing oscillator

ABSTRACT

An intervalometer for firing one or a group of ordnance devices comprises a normally self-stepping electromechanical solenoidoperated switching device and a separate independent timing oscillator. The oscillator is connected to the stepping switch to externally trigger initiation of each step of the switch and is arranged to permit substantially instantaneous actuation of the intervalometer upon receipt of the electrical fire command signal. Although normally instantaneously starting, the oscillator is provided with a delay to accommodate bounce time of pilot-operated firing switches. Continued oscillator operation in the event of temporary power dropout is provided.

United States Patent [72] Inventor Charles E. Everest Corona Del Mar,Calif. [21] Appl. No 62,948 [22] Filed Aug. 11, 1970 [45] Patented Nov.2, 1971 [73] Assignee William Wahl Corporation Los Angeles, Calif.

[54] INTERVALOMETER AND TIMING OSCILLATOR 22 Claims, 2 Drawing Figs.

[52] US. Cl 317/80, 89/1.814 [51] Int. Cl F23g 7/02 [50] Field of Search317/80; 102/702, 22; 89/1.8 14

[56] References Cited UNITED STATES PATENTS 2,421,893 6/1947 Lambert eta1. 89/1.814X 2,488,228 11/1949 Nims et a1 317/80 2,794,079 5/1957Ballet et al 317/80 X 2,832,265 4/1958 Reid et a1... 317/80X 2,853,5639/1958 Bole et a1.. 3l7/30X 3,064,537 11/1962 Baller et a1 89/l.8l43,453,496 7/1969 Wright et al. 317/80 3,468,255 9/1969 Stryker,.lr.102/702 Primary Examiner--Volodymyr Y. Mayewsky AttorneyGausewitz andCarr ABSTRACT: An intervalometer for firing one or a group of ordnancedevices comprises a normally self-stepping electromechanicalsolenoid-operated switching device and a separate independent timingoscillator. The oscillator is connected to the stepping switch toexternally trigger initiation of each step of the switch and is arrangedto permit substantially instantaneous actuation of the intervalometerupon receipt of the electrical fire command signal. Although normallyinstantaneously starting, the oscillator is provided with a delay toaccommodate bounce time of pilot-operated firing switches. Continuedoscillator operation in the event of temporary power dropout isprovided.

PATENTED 2 SHEET 10F 2 INVENTOR.

m mw INTERVALOMETER AND TIMING OSCILLATOR BACKGROUND OF THE INVENTION 1.Filed of the Invention This invention relates to the field ofelectromechanical devices and associated methods for controlling firingof rockets or other ordinance devices in predetermined sequence and withpredetermined times between firings, and more particularly concernsoperation of a normally self-stepping firing device by means of anindependent all-electronic triggering circuit.

2. Description of Prior Art Various types of rockets and other ordnancedevices such as flares, for example, are conventionally fired from theirlaunching devices either singly or in sequence or in a sequence ofpairs. Where the rockets are fired in sequence, it is essential that thesequential ignition and firing be precisely times. Although it isdesirable to fire the rockets of a group in as short a time as possible,where the rockets are to be fired individually and not collectively asin a salvo, it is essential that sufficient time between ignition ofsuccessively fired rockets be allowed to permit each rocket to clear itslaunching tube before triggering of the next ignition is begun. Failureto provide adequate periods between successive ignitions may cause onerocket to be fired too closely after a preceding rocket has been fired.This may result in damage to the rockets, bending or destroying fins ofone or both. At best, such damage will result in a rockets failure tostrike its target. At worst, such damaged rockets may explode closelyadjacent their launch tubes or may be so deflected as to return tostrike the launching system.

An additional disadvantage of successively fired rockets ignited atshort intervals derives from the high shock loads experienced by thelaunching equipment upon the launch of each rocket. Such shock load maybe as high as 500 gs and may have severe and adverse effects upon thefiring mechanism itself. In particular, it is highly desirable to avoidmotion of mechanical switch and camming parts of the firing mechanism atthe time of ignition, when such mechanisms are subjected to the maximumshock load. Accordingly, all of the moving parts of the firing mechanismare preferably in a temporary rest position and firmly retained in suchposition when the electrical firing pulses are applied to ignite theindividual rocket.

lntervalometers most commonly used at present are of two general types.The self-interrupting, self-stepping electromechanical stepping switchhas been widely employed for a number of years. Attempting to avoidproblems involved with mechanical devices, a second type, theall-electronic firing pulse distributing system, has been designed.

All-electronic intervalometers such as that shown in the U.S. Pat.3,316,451 issued Apr. 25, 1967 to R. L. Silverman for lntervalometerwill, in general, employ a timing oscillator and an all-electroniccommutator that provides a number of sequentially timed firing pulses tothe rocket igniters. Complexity, reliability, and high cost ofmanufacture of such allelectronic circuits are among their majordisadvantages.

The earlier designed and more widely used self-interrupting steppingswitches have been developed over a period of years to a point that hasbrought the cost of manufacture well below that of equivalentall-electronic apparatuses. Nevertheless, the electromechanicalself-interrupting and self-stepping switch sufiers from many drawbacks.Typical of such solenoidoperated stepping switches are the devices shownin U.S. Pats. to G. H. Leland, Nos. 2,496,880 and 2,501,950, and theU.S. Pat. to J. R. Davis, No. 3,384,728.

Employing the principles of these patents, C. C. Giese, Jr. et al. inU.S. Pat. No. 3,405,376 describes a stepping mechanism for a drivingrotary switch that includes an interrupter cam to cause the device tooperate much like a free-running oscillator. It automatically steps fromcontact to contact as long as power continues to be applied to itssolenoid-actuating coil. Briefly, the rotary stepping mechanism ofGlese,Jr. et al. comprises a rotary actuator that is driven through a segmentof are upon energization of a solenoid coil. Motion of the solenoidduring each step is stopped mechanically during such segmental rotation.Near the end of its travel a cam connected with the actuator temporarilyopens a switch that interrupts power to the driving coil. Uponinterruption of power, a return spring that is extended during thestepping action returns the actuator to its initial point and themechanism is cocked, having completed one cycle and begins its nextcycle, providing that the main power is still applied. In the course ofthe segmental rotation of the driven actuator, a ratchet is driven tosegmentally rotate or step one or more decks of rotary switch bankswhich accordingly may sequentially apply power to a group of ordnancedevices.

The solenoid operated switch mechanisms of the type described in theLeland and Davis patents are mechanisms of established operation, provenutility, and are available at relatively low cost. Nevertheless, thefree-running electromechanical version or self-interrupting switch asdescribed by Giese, Jr. et al. introduces a number of problems thatincrease its difficulty of manufacture and cost, and, further, seriouslydegrade reliability and operation of the intervalometer. Because theself-interrupting electromechanical stepping mechanism of Giese, Jr. etal. is largely a mechanical oscillator, the apparatus must be detunedand desensitized to the severe and repetitive shock and vibration ofrocket launching and airborne applications in general.

Major problems of the self-interrupting rotary stepping mechanism arisebecause of its natural frequency. it is found that switches of this typeoperate at a natural frequency having a natural period in the order of20 milliseconds. Such frequency is determined to a large extent by thesize and mass of the moving mechanical parts. However, since the partsare mass produced to minimize cost, it is exceedingly difficult if notimpossible to maintain a natural frequency of such a selfsteppingmechanism within any reasonable tolerance limits. in fact, in actualpractice, natural frequency of such switches for intervalometeroperation have been known to vary as much as percent.

Even the 20 millisecond nominal natural period is too small for optimumoperation of a sequentially fired bank of rockets. Accordingly, rocketsfired with such apparatus may be subject to inadvertent salvo firing;that is, where all are fired together. Alternatively, the rockets mayfire in such rapid sequence that they will physically interfere witheach other to thus totally destroy the intended trajectory or as hasbeen known to happen on occasion, to actually damage the firing aircraftitself.

In spite of this problem of relatively short and unpredictably variablenatural period of the self-stepping lntervalometer switch, the mechanismis so constructed and arranged that it is impossible to significantlyincrease the natural period of its self-stepping operation. It has longbeen known that no rocket in a sequence of rocket firing should beignited until the preceding rocket has cleared the launching tubes.Since ignition and acceleration of rockets are fairly predictable, it isknown that ignition of rockets to be fired in a sequence should bespaced by intervals of not less than about 60 milliseconds. Thus,optimum firing intervals are considerably greater than maximum naturalperiods of the commonly employed self-interrupting stepping switch.

Hybrid devices have been suggested, largely for the purpose of providinggreater flexibility and number of control functions and allowing moreintensive monitoring of the firing operation by the pilot who can thenvisually monitor the operation and condition of the apparatus at alltimes. Such a hybrid arrangement is shown in U.S. Pat. No. 3,453,496 forFire Control lntervalometer to J. B. Wright, et al. in the arrangementshown by Wright, both electrical and mechanical parts of the steppingswitch mechanism itself inherently form parts of the timing oscillatorand accordingly, the mechanical parts to some degree control the periodof operation. Nevertheless, there is provided by Wright an electroniccircuit that does afford additional flexibility of control of timing.

Although Wright provides a separate and selectively operable timingcircuit that enables selection of a different number of rockets forfiring, the basic timing is provided by an oscillator coil and theself-interrupting switch contacts of the stepping switch itself.Accordingly, this arrangement fails to adequately isolate fundamentalfrequency defining components from the mechanical parts of themechanism. Furthermore, the arrangement of Wright suffers from adrawback that is common to all of the previously describedelectronically controlled intervalometer operations. This is theinability to precisely control the time of firing of the first rocket ofa sequence.

According to military requirements, the first rocket of a sequence mustbe fired within 20 milliseconds of completion of the firing circuit bypilot operation of the firing button.

This requirement for near instantaneous and controlled initial turn-onoperation introduces even greater problems and complexity of circuitryin the all-electronic or all-electronically timed intervalometer. Asindicated above, the preferably natural period for such an electronictimer is in the order of 60 milliseconds. Although this period is anoptimum requirement, it will not meet the military specification thatrequires a substantially instantaneous firing of the first rocket.Relaxation oscillators, astable multivibrators and other free-runningoscillators will provide an output pulse after initial energization thatoccurs upon completion of a first half cycle of the oscillator. Forhighly asymmetrical oscillators such as the ordinary unijunctiontransistor relaxation oscillator, the output pulse occurs only after thetiming capacitor has fully charged which may take up to 99 percent of afull complete cycle. Thus, although the conventional oscillator may bereadily timed to provide a 60 millisecond natural period, such a periodhas not been available from an apparatus capable of substantiallyinstantaneous turn on operation.

Because of the arrangement of the fire control wiring in the ordinaryaircraft, there may be as may as to 12 switches and detachableelectrical connections between the pilot operated fire control buttonand the intervalometer itself. Over a period of time and as theapparatus is subjected to repeated and continuous use and vibration ofaircraft operation, such switch contacts and connectors wear and becomeloose whereby ordinary vibration of aircraft operation will inducemotion of switch and contact parts. Thus, when the pilot depresses thefiring button, one or more of these switches and contacts may bevibrating and be subjected to switch bounce to thereby introduce severetransients into the control signal that may last from 1 to 2milliseconds. This switch bounce is detrimental to the initial operationthat occurs upon the first energization of the solenoid coil of theconventional rotary stepping switch.

Accordingly, it is an object of the present invention to provide asubstantially self stepping electromechanical intervalometer switch witha timing oscillator that will reliably provide the intervalometer with adesired firing interval and at the same time afford a controlledsubstantially instantaneous turn on of the intervalometer.

SUMMARY OF THE INVENTION In carrying out the principles of the presentinvention in accordance with a preferred embodiment thereof a steppingswitch having a driving coil connected to be energized by a power supplythrough a self-interrupting switch in circuit therewith, is providedwith an externally triggered coil energizing switch that is arranged tobe closed by receipt of an external trigger to initiate energization ofthe driving coil which has its energization interrupted in aconventional fashion by its interrupter switch. The coil-energizingswitch is triggered by an oscillator at the desired intervalometerrepetition rate. The oscillator is uniquely arranged to provide itsfirst output trigger pulse to the coil-energizing switch substantiallyimmediately upon application of power to the circuit. A switch bouncedelay in operation of the first oscillator trigger pulse is alsoavailable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a preferredembodiment of an intervalometer incorporating a timing oscillatorconstructed in accordance with the principles of the present invention,and

FIG. 2 comprises an illustration of a modification of circuit of FIG. 1.cDETAILED DESCRIPTION The present invention in accordance with thepreferred embodiment illustrated and described herein basicallycomprises a self-stepping rotary switch and a timing oscillator forcontrolling the switch. The rotary switch may be of the type describedin the above-identified Leland and Davis patents and, in particular,will include a self-interrupting mechanism for providingself-interrupted power to the solenoid as described in theabove-identified U.S. Pat. to C. C. Giese, Jr. et al. No. 3,405,376, thedisclosure of which is fully incorporated herein by reference.

Portions of such a stepping switch are schematically shown in FIG. 1.Briefly, the self-interrupting rotary stepping switch of Giese comprisesa DC voltage supply 10 that supplies power to a solenoid stepping coil12 of the electromagnetic actuator via a manual pilot-controlled firingbutton 14, a first safety or arming deck 16 and a set of interrupter andfiring switch contacts i8.

Ignoring at this time other elements in circuit with the electromagneticactuator coil 12, it will be seen that the firing of the intervalometeris enabled (the device is armed) by manually moving the intervalometerswitch through its first two steps, from the illustrated "load" positionof first safety deck 16 to an arm" position by manual means notillustrated. In the illustrated load, or first safety position, firstswitch deck 16 provides an open circuit in the power supply to thesolenoid coil because the switch arm 19 does not make contact in thisposition with the conductive surface of the deck 16. In all otherpositions of the switch and of the deck 16, the pilot operated closingof firing switch 14 will provide the full 28 volts of the power supplyat point 20 for transmission by the interrupter switch 18 to thesolenoid actuating coil 12.

Considering the rotary switch decks to be in arm position, closing offiring switch 14 energizes solenoid coil 12 to thereupon initiate thefirst segmental rotational step of the switch decks. These rotatethrough about 30 and are mechanically stopped. As more particularlydescribed in detail in the Giese patent, as the actuator travels throughits 30 throw the interrupter cam operates to momentarily move an arm 22of the interrupter switch from its electrically contacting position withcontact to momentarily contact with a firing contact 24. Since thismomentary contact of interrupter switch arm 22 and contact 24 occurs ator near the end of the thirty degree actuator throw, the various switchdecks have already been stepped to their new position and are preferablyat rest. Accordingly, in such switch position, a relatively short firingpulse is provided from the DC supply via the closed fire control button14 through deck 16, arm 22 and contact 24 of the interrupter switch, toa fire sequencing switch deck 26. Switch deck 26 in addition to having apair of commonly grounded load and arm contacts has six rocket firingcontacts in the simplified illustration, identified as 27, 28, 29, 30,31 and 32. Each of the latter is connected to ground through arespective one of the schematically depicted rocket ignition circuits33, 34, 35, 36, 37 and 38.

A third switch deck 40 provides a second safety operation and has inaddition to load and arm positions six contacts designated as 270through 324:, each of which is connected to a correspondingly numberedcontact of the second switch deck 26. The body of third deck 40 isconnected to ground whereby all of the input lines to the rocketignition circuits 33 through 33 are always grounded except when aparticular one of the contacts 27a through 32a is adjacent the indentedportion of the deck 40, whereby it is freed of its ground connection.

From this brief description of the stepping switch decks, it will beseen that the cam-operated throw of interrupter switch arm 22 intomomentary engagement with contact 24 provides a firing pulse to that oneof the rocket ignition circuits 33 through 38 that is selected by theparticular position of the several switch decks at such instant.Accordingly, one rocket and only one rocket will be fired.

The second function of the interrupter switch 22, 24, which occurssimultaneously with the transmission of the rocket-firing pulsetherethrough, is the interruption of the power circuit from point 20 ofdeck 16 to the switch 18 to the solenoid stepping coil 12. When thiscoil is deenergized, a spring that has been tensioned during the poweredrotary throw of the switchactuator returns the latter to a rest orcocked position and the apparatus has completed a single full cycle.

In the absence of any further circuitry or components, and in theabsence of the parts of the invention timing circuit that will bedescribed hereinafter, power is still applied from DC supply via thestill closed fire command button 14, via safety deck 16, and through arm22, contact 23 of the interrupter switch which had been immediatelyreturned to its normal position (illustrated). Accordingly, solenoidcoil is once again energized, its actuator driven and its switch deckstepped through a 30 segment of rotation. In this new position, a secondone of the rocket-firing contacts 27 through 32 is in contact with thefiring deck 26 and freed from its safety ground connection of switchdeck 40 whereby it is ready to accept a firing pulse. This firing pulseis provided via the interrupter switch 18 and its arm 22 which ismomentarily moved during travel of the actuator to engage contact 24.The second rocket is fired, coil 12 is deenergized and returned to itscocked position and arm 22 returns to its normal position whereuponanother cycle has been completed.

As previously described, the natural period of the abovedescribedrepetitive and cyclic switch operation is in the order of 20milliseconds and furthermore, may vary with normal manufacturingtolerances by as much as 100 percent. This 20 millisecond period isconsiderably less than the desired 60 millisecond interval betweenfiring of successive rockets and cannot be significantly increased in arotary stepping switch of any reasonable size or of any reasonabledegree of compactness. Consequently, even if the high degree ofvariation of the natural period could be tolerated, the short period andhigh frequency of operation is still unacceptable.

In accordance with principles of the present invention, maximum use ismade of the highly developed mechanical arrangement of theelectromechanical self-interrupting stepping switch, described herein.At the same time its most serious disadvantages are eliminated. To theseends there is provided a second switch, a coil-energizing switch 42, inseries circuit with the coil 12, its interrupter switch 18, and thepower supply 10. Coil-energizing switch 42 is illustrated in the form ofa silicon-controlled rectifier (SCR) having an anode 43 connected to oneside of coil 12 and having a cathode 44 connected to ground which formsthe other side of the power supply 10. Coil-energizing switch 42 has atriggering electrode, the SCR control electrode 45, that is arranged toreceive a trigger pulse from an oscillator 46 that defines and providesthe overall timing of the illustrated intervalometer. Frequency of theoscillator is considerably less than the natural frequency of thestepping switch.

Coil energizing switch 42 is a conventional SCR that provides a normallyopen circuit between its anode 43 and cathode 44 until it has beenactuated or turned on. It is actuated by a receipt of a trigger pulse atits control electrode 45. Once it has been actuated and even though allsignals are withdrawn from its control electrode 45, it provides asubstantially low-resistance circuit between its anode 43 and cathode 44to thereby, in effect, connect the lower end of coil 12 to ground. Thislow-resistance circuit continues to connect the coil to ground unlessand until anode current to the SCR 42 is interrupted.

Consequently, once triggered by a signal at control electrode 45, SCR 42continues to ground the lower end of coil 12 until power to the coil isinterrupted by operation of interrupter switch 18. Thus, each cycle ofthe stepping switch is terminated by the interrupter switch 18 just asif the stepping switch was entirely free-running and independent of anyexternal control. The difference is, however, that once any cycle hasterminated, the next cycle does not and cannot commence until thecoil-energizing switch 42 has been once again triggered.

Each stepping switch cycle is initiated by an external trigger signaland terminated by internal mechanisms. The external trigger signal forinitiating operation of each stepping switch cycle is provided byoscillator 46 comprising a unijunction transistor 48 having a base oneelectrode 49 connected to a positive supply line 50 and a base twoelectrode 51 connected to the control electrode 45 of thecoil-energizing switch 42. A primary RC timing circuit of the oscillatorcomprises a capacitor 52 and a resistor 53 that are connected as aparallel RC circuit between the emitter electrode 54 of the unijunctiontransistor and the positive supply line 50. lnterposed between the RCtiming circuit 52, 53, and line 50, is a second resistor 55. A bouncedelay and power storage capacitor 56 is connected between ground and thepower line 50 through resistor 55.

The illustrated oscillator arrangement provides a uniquely timedrelaxation oscillator having an oscillator switch formed by transistor48 that will provide an output pulse substantially immediately uponreceipt of power thereto. Although primary timing of the oscillatorcycle, that is, the length of each of its periods, is controlled by RCtiming circuit 53, 52, delay of the first pulse, and only of the firstpulse, is achieved by use of the switch bounce capacitor 56. The lattereffects a delay only of the first oscillator cycle and, therefore, ineffect, achieves a phase delay of an entire series of successiveoscillator cycles.

Power is supplied to oscillator 46 via power line 50 and a PNPtransistor 58 having its collector connected to the oscillator powersupply line 50 and its emitter connected to point 20 at which a positiveDC voltage is supplied from source 10.

Connected to the base of transistor 58 is a series connected resistor 59and a zener diode 60. The anode of zener diode 60 is connected toground. This circuit, comprising resistor 59 and zener diode 60,protects the oscillator 46 from inadvertent operation that may be causedby stray or spurious voltages, in the order 149 138 volts or less wherea standard 28 volt source 10 is sued. Zener diode 60 is chosen so thatit will fire and conduct only when a voltage somewhat less than thechosen level of 18 volts is provided thereacross. Accordingly, unlessand until the voltage at the emitter of transistor 58 rises to a pointat least one diode drop, (about one-half volt) above the voltageestablished by the zener diode 60, the latter will not conduct and thebase of transistor 58 will draw no current. Transistor 58 is and remainscut off until voltage at its emitter rises above 18 volts. With thisarrangement, the circuit is particularly arranged for operation with theconventional 28 volt DC military supply source and protected againstinadvertent operation in the presence of stray voltages of 18 volts orless.

In operation, when the pilot closes firing button 14, power is suppliedvia deck 16 and point 20 through transistor 58, through resistor 55, toone side of the primary timing capacitor 52. However, since the voltageacross the capacitor cannot change instantaneously, this primary timingcapacitor will instantaneously (assuming for this part of thedescription that capacitor 56 is not connected) transmit to the emitterelectrode 54 of the unijunction transistor 48, the high level of DCvoltage that suddenly occurs upon closing of the firing button 14. Itshould be noted at this point that the conventional relaxationoscillator and the conventional unijunction transistor version of therelaxation oscillator ordinarily has its primary timing capacitorconnected between the transistor or oscillator-switching device controlelectrode and ground. Thus, in a conventional oscillator noinstantaneous voltage-transmitting circuit such as primary timingcapacitor 52 is connected between the power supply and the transistorcontrol electrode. Accordingly, with such a conventional device. thetransistor control electrode will not see a voltage sufficient to causeit to conduct unless and until its timing capacitor becomes fullycharged. In the ordinary relaxation oscillator, this time for fullycharging the main timing capacitor is a significant portion and oftenwell over 90 percent of the entire total period of the oscillator. Forthis reason, if one were to use the usual relaxation oscillator as atiming device for generating trigger pulses to actuate coil-energizingswitch 42, coil 12 could not begin to be energized until nearly 60milliseconds after operation of fire control button 14, and because ofthe built-in and inherent delay of the electromagnetic steppingmechanism itself, the firing of the first rocket would be still furtherdelayed. Such delay does not comply with military specifications.

A simple, reliable and inexpensive circuit to avoid this undue delay isthe illustrated arrangement of connecting the main timing capacitorbetween the unijunction transistor emitter and the power line 50. Thus,as power line voltage steps up immediately upon closing of the firingbutton 14, the emitter 52 reaches a voltage sufficient to triggerconduction of the unijunction transistor whereby current flows from thepower line via main timing capacitor 52 through the emitter base oneelectrodes of unijunction transistor and to the control electrode 45 ofsilicon-controlled rectifier 42. The latter thereupon goes intoconduction and the current path through coil 12 is then completedthrough the cathode of the SCR to ground.

As the SCR conducts the lower end of solenoid coil 12 is grounded and,accordingly, a path is completedthrough the coil 12 through theinterrupter switch 18 in its normal position, through switch deck 16,and firing button 14 to the power supply 10. Thus, the first cycle ofthe electromagnetic stepping switch is initiated immediately uponclosure of the fire control button 14.

As indicated above, the stepping switch terminates its own cycle byoperation of interrupter contacts 18 whereby power to the anode 43 ofSCR 42 is interrupted and the latter goes into its nonconducting state.

During the driven segmental rotation of the stepping switch actuator andbefore interrupter switch 18 was actuated to disconnect the SCR anodefrom power supply, the instantaneous initial surge of current providedvia primary timing capacitor 52 to the emitter electrode 54 ofunijunction transistor 48, decreased rapidly below the value of theholding current required to maintain unijunction transistor 48 in itsconducting state. Accordingly, the unijunction transistor 48 is turnedoff and conducts no further current to the gate electrode 45.Consequently, the latter, when its anode current is shot ofi byinterrupter switch 18, remains nonconducting.

Thus, the first external trigger has been supplied substantiallyinstantaneously (except for the switch bounce delay to be described), astepping switch cycle has been initiated and has been self-terminated.Coil energizing switch 42 is open and the circuit now must wait for thenext trigger pulse from the oscillator 46, even though firing button 14remains closed.

At the end of this first cycle, emitter 54 of the unijunction transistor48 is at a low voltage, being above ground by an amount only equal tothe relatively small voltage drops across the several electrodes of theunijunction transistor 48 and the SCR 45. When transistor 48 stopsconducting, capacitor 52 beings to charge via main timing resistor 53,the latter having a relatively large value in the order of 124,000 ohms,whereby the junction of capacitor 52 and emitter 54 of transistor 48begins to rise. After lapse of the time period of the oscillator 46,which is established at 60 milliseconds as previously described, thejunction of capacitor 52 and emitter 54 has been raised to a voltagelevel that is about 60 percent of the base one to base two voltage ofthe unijunction transistor. This is the voltage at which the latter willconduct, whereupon a second trigger signal is fed from the base twoelectrode of the unijunction to the control electrode 45 of the SCR. TheSCR conducts to once again initiate energization of coil 12 and a secondfull cycle of the stepping switch.

Thus, it will be seen that the first cycle of the stepping switch isalmost instantaneously triggered upon turn on of the apparatus and thesubsequent triggering pulses are received at 60 millisecond intervals.

Because of the many switches and contacts that are wired into theconventional aircraft between the pilot's fire control button and theintervalometer, the power supply signal fed to the oscillator and to theintervalometer is subject to l to 2 milliseconds of startup transientsas previously described. If the oscillator circuit should be turned oninstantaneously and start its operation, and thereafter during the next1 to 2 milliseconds the power line transients due to switch bounceshould momentarily withdraw power, operation and timing of the mechanismwill be seriously hampered. Accordingly, full instantaneous applicationof energizing power to the oscillator is not desirable. A small amountof delay, in the order of l to 2 milliseconds to allow transients causedby switch bounce to settle out, is accordingly provided by the use ofcapacitor 56 connected between ground and power line 50. Capacitor 56cooperates with resistor 55 to provide the relatively small amount ofdelay in the initial rise of voltage at emitter 54. The time constant ofthe circuit including resistor 55 and capacitor 56 is relatively smallsince resistor 55 may be in the order of 2,200 ohms, a valueconsiderably less than the value of the primary timing resistor 53.Thus, upon initial operation of the firing button 14, switch bouncecapacitor 56 provides a short delay but is rapidly charged to thevoltage required to fire the unijunction transistor 48. With theillustrated arrangement, switch bounce capacitor 56 has a negligibleaffect upon operation of the circuit subsequent to the generation of thefirst oscillator trigger signal except for its storage function, to bedescribed below.

Provision is made for firing the rockets singly to thereby override theripple or sequence firing previously described. This operation isachieved by actuation of a ripple switch 41. In the illustrated openposition of this switch, all of the rockets connected to the sequencerstepping switch will be fired in sequence by the described cyclicoperation. When ripple switch 41 is closed, interrupter switch contacts22, 23, are bypassed, whereby only a single rocket will fire as long aspilot button 14 is held in closed position.

With ripple switch 4] closed, the power is supplied directly to the topend of coil 12 to FIG. 1 to thereby bypass interrupter switch 18 in thepower application line. Accordingly, even though interrupter switch 18will be thrown momentarily to fire a single rocket, when it does throw,it will not interrupt power to the coil 12. The latter will remainenergized and cannot be returned to its cocked position until powerthereto is disconnected by release of firing switch 14.

Military specifications allow relatively wide variation in airborne DCpower supplies. In addition to transients and fluctuations in powersupply level, the specifications permit momentary loss of power from thesupply. Obviously, a loss of power, even if momentary, could seriouslydisrupt any ongoing timing sequence of rocket firing. To compensate thistemporary loss of power to the oscillator 46, switch bounce capacitor 56is connected as illustrated in FIG. 1 and made as large as is possiblewithin the space limits of the intervalometer apparatus.

Accordingly, in addition to its operation to provide a l or 2millisecond delay in cooperation with delay resistor 55, capacitor 56will charge to the voltage on line 50 during any firing sequence andmaintain such charge. Should there be a momentary dropout in line power,such that power is no longer supplied from the DC supply 10 to therelaxation oscillator transistor 48, such power may be provided by thecharge stored in capacitor 56. This capacitor remains charged because ofthe unidirectional characteristics of the spurious and transient voltageprotection transistor 58. The latter acts as a diode to prevent anycharge on capacitor 56 from being discharged back through the powersupply in the event of momentary dropout of the latter. To retain thisunidirectional isolating function of transistor 58 in those arrangementswhere its spurious or transient voltage protection functions are notrequired, the transistor 58 may simply be replaced with a suitably poleddiode in order to ensure retention of sufficient charge on capacitor 56.

It may be noted that this operation of capacitor 56 to retain anoscillator driving charge in the event of power supply dropout in no waycompromises or adversely affects its other provided by transistor 58,resistor 59, and zener diode 60 of FIG. 1. In its stead, a voltageregulating circuit comprising substantially similar components, butconnected for a different function, is employed. Further, a differentconnection for the switch bounce capacitor is employed.

Electromechanical portions of the self-interrupting stepping switch, asschematically illustrated in FIG. 2 and corresponding to similar partsof FIG. 1, are designated by corresponding reference numerals prefixedby the number 1. Thus, coil 112 of FIG. 2 is equivalent to coil 12 ofFIG. 1 and switch deck'l 16 of FIG. 2 is equivalent to switch deck 16 ofFIG. 1.

The mechanical stepping switch of FIG. 2 includes a DC supply 110providing voltage through a fire control button 114 and a switch deckI16 to an interrupter switch 118 which also connects with and providesfiring signals to a group of switch decks and firing circuitscollectively illustrated at 133 and constructed and arranged just thesame as corresponding parts of the embodiment of FIG. 1.

An SCR 142 is provided in series circuit with the coil 112 and arrangedto receive a trigger signal from a unijunction transistor relaxationoscillator 146. All of the elements thus far identified in FIG. 2 areidentical in construction, arrangement and operation to thecorresponding elements of the embodiments of FIG. 1.

In the embodiment of FIG. 2, the transistor 158 is interposed hetweenthe oscillator power line 150 and the power line provided at the output126 of the first safety switch deck 116. This transistor is an NPNtransistor and its position is reversed in order to allow it to performits operation as a voltage regulator. Its emitter is connected to theoscillator and its collector is connected to receive power from thesupply line at point 120. Transistor 158 has its base connected toground via a zener diode 160. A resistor 159 is connected between thetransistor base and collector.

Zener diode 160 is chosen with such rating that it will not conduct viaresistor 159 as long as the power supply provided to the collector ofNPN transistor 158 is substantially at or not greatly above the 20 voltsupply level. However, should the notoriously fluctuating aircraftsupply source provide higher voltage, such higher voltage is transmittedto the zener via resistor 159 and the zener will conduct to maintain thebase of transistor 158 at a substantially maximum level above ground. Inother words, high-level transient signals at the transistor collectorare shunted to ground via the zener. Accordingly, the power supplyprovided to the oscillator at the emitter of transistor 158 is regulatedand oscillator frequency and stability thereby greatly enhanced.

In the embodiment of FIG. 2 there is shown a variation in connection ofthe switch bounce capacitor 156. This capacitor now performs solely theinitial time delay and participates with timing capacitor 152 in thesteady-state cyclic timing of the oscillator. Initial step-up ofvoltage, upon turn on, at the power side of capacitor 152 is stored incapacitor 1156. Consequently, rise of voltage at the emitter oftransistor 148 is delayed for I to 2 milliseconds by the action ofresistor 155 and capacitor 156.

With the capacitive divider connection of capacitors 152, 156, as shownin FIG. 2, both control voltage on the emitter of the unijunctiontransistor, and both are charged through resistor 153 to control theoscillator period.

It will be understood that the connection of timing capacitors of eitherFIG. 1 or FIG. 2 can be used with either of the voltage regulator orspurious voltage protection transistors 158, 58, or vice versa.

There has been described a new and unique intervalometer that employs along developed electromagnetic self-interrupting stepping switchtogether with a novel control circuit that makes optimum use ofdesirable features of the stepping switch and avoids its majordisadvantages. The control circuit operates to initiate energization ofthe stepping switch driving coil at precisely controlled andindependently variable repetition rate, independent of the mechanicalswitch elements. The timing control circuit is arranged to permitsubstantially instantaneous turn on of the stepping switch energization,to allow the intervalometer to meet the military requirement of firing arocket within 20 milliseconds of the firing command, and at the sametime provide sufficient delay to avoid deleterious efiects of switchbounce.

The foregoing detailed description is to be clearly understood as givenby way of illustration and example only, the spirit and scope of thisinvention being limited solely by the appended claims.

I claim:

ll. An intervalometer for providing electrical firing signals in aselected sequence and at a selected frequency to a group of ordnancedevices, said intervalometer comprising:

a power supply,

a solenoid-operated stepping switch for sequentially supplyingelectrical pulses from said power supply to said ordnance devices,

a solenoid-coil-energizing switch for controlling application ofenergizing electrical power to said solenoid-operated switch, and

a timing oscillator for operating said solenoid-coil-energizing switchwith a controlled turn on delay and thereafter with a preselectedsteady-state repetition rate, said oscillator comprising an oscillatorswitch having an output connected to actuate saidsolenoid-coil-energizing switch, and having a triggering input, anoscillator storage device for initially effecting a substantiallyinstantaneous transmission of power supply voltage to said triggeringinput of said oscillator switch when said power supply is turned on,said storage device including means for effecting a charging thereof ata selected rate and to a value sufficient to again trigger saidoscillator switch, said oscillator storage device being connected to bedischarged by said oscillator switch when the latter is operated, meansfor effecting a controlled initial delay of the application of a voltagefrom said power supply to said oscillator switch through said storagedevice, whereby said oscillator switch is triggered after a relativelyshort interval following initial turn on of the power supply and isthereafter triggered at relatively longer intervals each determined bythe time required to charge said storage device, and whereby saidsolenoid-coil-energizing switch is actuated each time said oscillatorswitch is triggered.

2. The intervalometer of claim 1 wherein said oscillator switchcomprises a unijunction transistor having an emitter, and wherein saidoscillator storage device comprises a parallel resistance capacitancecircuit connected between the power supply and said emitter.

3. The intervalometer of claim 2 wherein said solenoid-coilenergizingswitch comprises a silicon-controlled rectifier having an anodeconnected with a coil of the solenoid, having a cathode connected to acommon line, and having a control electrode, and wherein saidunijunction transistor includes a base one electrode connected to saidpower supply and a base two electrode connected to said controlelectrode of the silicon-controlled rectifier.

4. The intervalometer of claim 3 wherein said means for effecting acontrolled delay of the first application of said supply voltage to theoscillator-switching device comprises a delay capacitor connectedbetween said common line and one side of said parallel resistancecapacitance circuit.

5. The intervalometer of claim 4 wherein said delay capacitor isconnected between said common line and the emitter of said unijunctiontransistor.

6. The intervalorneter of claim 4 wherein said delay capacitor isconnected between said common line and the junction of said power supplywith said resistance capacitance circuit, and wherein a unidirectionaldevice is connected between said power supply and said delay capacitor,whereby in the event of temporary power supply dropout, said delaycapacitor will retain a charge sufi'icient to continue operation of saidoscilla- I01.

7. An electronically timed mechanical intervalometer for sequentiallyfiring a group of ordnance devices, said intervalometer comprising:

a plurality of banks of switches,

a solenoid connected to drive said banks of switches,

said solenoid having an energizing coil and a set of self-interruptingcontacts therefor,

a coil-energizing switch for repetitively energizing said solenoid coil,and

an oscillator for repetitively closing said coil-energizing switch, saidoscillator comprising a unijunction transistor having a base oneelectrode connected to said power supply, having a base two electrodeconnected to a controlling terminal of said solenoid-coil-energizingswitch, and having an emitter electrode,

a main timing capacitor having one side thereof connected to saidemitter electrode of said unijunction transistor,

a first resistor connected between one side of said power supply and theother side of the timing capacitor, a second resistor connected inparallel with said capacitor, and

a delay capacitor connected between the other side of said power supplyand one side of said main timing capacitor.

8. The intervalometer of claim 7 wherein said capacitors comprise acapacitive voltage divider connected between a junction of said firstand second resistors and said other side of the power supply,

said voltage divider having a tap connected to said emitter electrode ofthe unijunction transistor.

9. The intervalometer of claim 7 wherein said delay capacitor isconnected between said other side of said timing capacitor and saidother side ofsaid power supply.

10. In an intervalometer having a stepping switch connected to fire agroup of ordnance devices in sequence, said stepping switch having asolenoid and solenoid-energizing coil adapted to be energized through acoil-energizing switch from a power supply for incrementally rotatingthe switch, the improvement comprising a timing oscillator forperiodically energizing said solenoid coil at a selected repetition ratein a sequence of energizations that begins substantially instantaneouslyon application of power from said power supply, said timing oscillatorcomprising an oscillator switch having an output connected to operatesaid coil-energizing switch and having a triggering electrode connectedto be substantially isolated from steadystate levels of said powersupply and to respond to sharply rising increases thereof as occur uponturn on of the power supply,

an RC timing circuit connected to be charged from said power supply andto provide a triggering signal to said triggering electrode uponattainment of a predetermined voltage level, said timing circuitconnected to be discharged by actuation of said oscillator switch,whereby said oscillator switch and said coil energizing switch areactuated substantially instantaneously upon turn on of the 2,.. powersupply and intermittently thereafter each time said timing circuitattains said predetermined charge. 1 1. In an intervalometer having astepping switch connected to fire a group of ordnance devices insequence, said stepping switch having a solenoid-energizing coil adaptedto be energized through a coil-energizing switch, the improvementcomprising a timing oscillator for periodically initiating energizationof the solenoid coil at a selected repetition rate in a sequence ofenergizations that begins substantially instantaneously upon applicationof power from said power supply, said oscillator comprising anoscillator switch having an output electrode connected to actuate saidcoil-energizing switch, and having an input electrode arranged totrigger said oscillator switch upon attainment of a predetermined signallevel at said input electrode, a capacitor connected in series circuitwith said power supply and said input and output electrodes of saidoscillator switch, whereby a sudden increase in voltage of said powersupply, as occurs upon turn on of the circuit, is transmitted to saidinput electrode of the oscillator switch substantially instantaneously,and said capacitor is discharged by current conducted from said input tosaid output electrodes of said oscillator switch, and a charging circuitconnected to charge the capacitor from said power supply when saidoscillator switch is nonconducting, whereby after the first actuation ofthe oscillator switch that occurs substantially instantaneously uponturn on of the power supply, the oscillator switch will be operatedperiodically upon recharging of the capacitor through said chargingcircuit. 12. The intervalometer of claim 11 including a second capacitorconnected with said first-mentioned capacitor to form a capacitivevoltage divider connected across said power supply and having a tapthereof connected to said input electrode of said oscillator-switchingdevice.

13. The intervalometer of claim 11 including a second capacitorconnected to momentarily delay the sharp rise of voltage transmittedthrough said first capacitor to said input electrode of theoscillator-switching device upon turn on of the power supply, saidsecond capacitor being connected between said input electrode of theoscillator-switching device and ground.

14. The intervalometer of claim 11 including a second capacitorconnected to momentarily delay the sharp rise of voltage transmittedthrough said first capacitor to said input electrode of theoscillator-switching device upon turn on of the power supply, saidsecond capacitor being connected between ground and said power supply,and a unidirectional conducting device series connected between saidsecond capacitor and said power supply to enable said second capacitorto store and retain a charge sufficient to power said oscillator in theevent of temporary dropout of said power supply.

157 An intervalometer for providing electrical firing signals at aselected frequency and in a selected sequence that starts substantiallyinstantaneously upon a firing command for firing a group of ordnancedevices, said intervalometer comprising:

a power supply and a firing switch connected thereto, a stepping switchincluding a driving coil connected to be energized by said power supplythrough said firing switch,

an interrupter switch in circuit with said coil between said firingswitch and the coil for momentarily disconnecting the coil from thepower supply after the coil has been energized and upon substantialcompletion of one step of the stepping switch,

an externally actuated coil energizing switch connected in seriescircuit with said coil and power supply to initate energization of thecoil upon actuation of said coil-energizing switch and to maintain suchenergization until said interrupter switch is operated to disconnectsaid coil from said power supply and firing switch, whereby the coil isenergized by each actuation of said coil-energizing switch and is selfdeenergized by operation of said interrupter switch.

16. The intervalometer of claim including an oscillator connected to beenergized from said power supply and fire control switch for providing acyclically repetitive output trigger at the beginning of each cycle ofthe oscillator and for providing a first output trigger signalsubstantially immediately upon application of power to the oscillatorfrom the power supply and fire control switch, the output of saidoscillator being connected to actuate said coil-energizing switch intoconductive condition to thereupon initiate energization of said solenoidcoil.

17. The intervalometer of claim 16 wherein said oscillator has a naturalfrequency considerably less than the natural frequency of said steppingswitch whereby after each energization of the stepping switch coil thatoccurs upon actuation of the coil energizing switch, the coil is selfdeenergized by operation of the interrupter switch and remainsdeenergized until the coil-energizing switch is once again actuated bythe output of said oscillator.

18. The intervalometer of claim 17 wherein said coil-energizing switchcomprises a silicon-controlled rectifier having an anode and cathodeconnected in series circuit with said solenoid coil and having a controlelectrode, and wherein said oscillator comprises a unijunctiontransistor relaxation oscillator that includes a base two electrodeconnected to the control electrode of the silicon-controlled rectifier.

19. The intervalometer of claim 17 wherein said coil energizing switchcomprises a silicon-controlled rectifier having an anode and cathode inseries circuit with the solenoid coil and having a control electrode,and wherein said oscillator comprises a unijunction transistor having abase one electrode connected to said power supply and fire controlswitch, and having a base two electrode connected to said controlelectrode of the silicon-controlled rectifier and having an emitterelectrode,

a capacitor connected between said emitter electrode and the powersupply and firing switch, and

a charging resistor connected across the capacitor.

20. The intervalometer of claim 19 including a second capacitorconnected between said power supply and ground, and

a second resistor series connected between said second capacitor andsaid power supply and firing switch, whereby the sharp rise in voltageoccurring upon closing of the firing switch is applied to said emitterelectrode substantially instantaneously across said first capacitor, butis momentarily delayed in application to the emitter by means of thedelaying action of the second resistor and second capacitor so as toprevent operation of said unijunction transistor for a short period inthe order of the time required for switch bounce.

21. The intervalometer of claim 20 including a voltageregulatingtransistor connected between said s second resistor and said firingswitch,

said voltage-regulating transistor having a base electrode, a

zener diode connected to said base electrode for establishing asubstantially constant voltage level at such base electrode, and

a third resistor connected across the collector and base electrodes ofthe voltage-regulating transistor.

22. The intervalometer of claim 20 including a spurious voltageprotection circuit connected between the said oscillator and said powersupply and firing switch,

said protection circuit comprising a protection transistor havingemitter and collector electrodes connected between said second resistorand said firing switch and having a base electrode, and

a zener diode connected between the base electrode and ground, wherebysaid protection transistor will not conduct until a signal at one ofsaid collector and emitter electrodes rises above a predeterminedpotential level established by said zener diode and the voltage dropacross said protection transistor.

1. An intervalometer for providing electrical firing signals in aselected sequence and at a selected frequency to a group of ordnancedevices, said intervalometer comprising: a power supply, asolenoid-operated stepping switch for sequentially supplying electricalpulses from said power supply to said ordnance devices, asolenoid-coil-energizing switch for controlling application ofenergizing electrical power to said solenoid-operated switch, and atiming oscillator for operating said solenoid-coil-energizing switchwith a controlled turn on delay and thereafter with a preselectedsteady-state repetition rate, said oscillator comprising an oscillatorswitch having an output connected to actuate saidsolenoid-coil-energizing switch, and having a triggering input, anoscillator storage device for initially effecting a substantiallyinstantaneous transmission of power supply voltage to said triggeringinput of said oscillator switch when said power supply is turned on,said storage device including means for effecting a charging thereof ata selected rate and to a value sufficient to again trigger saidoscillator switch, said oscillator storage device being connected to bedischarged by said oscillator switch when the latter is operated, meansfor effecting a controlled initial delay of the application of a voltagefrom said power supply to said oscillator switch through said storagedevice, whereby said oscillator switch is triggered after a relativelyshort interval following initial turn on of the power supply and isthereafter triggered at relatively longer intervals each determined bythe time required to charge said storage device, and whereby saidsolenoid-coil-energizing switch is actuated each time said oscillatorswitch is triggered.
 2. The intervalometer of claim 1 wherein saidoscillator switch comprises a unijunction transistor having an emitter,and wherein said oscillator storage device comprises a parallelresistance capacitance circuit connected between the power supply andsaid emitter.
 3. The intervalometer of claim 2 wherein saidsolenoid-coil-energizing switch comprises a silicon-controlled rectifierhaving an anode connected with a coil of the solenoid, having a cathodeconnected to a common line, and having a control electrode, and whereinsaid unijunction transistor includes a base one electrode connected tosaid power supply and a base two electrode connected to said controlelectrode of the silicon-controlled rectifier.
 4. The intervalometer ofclaim 3 wherein said means for effecting a controlled delay of the firstapplication of said supply voltage to the oscillator-switching devicecomprises a delay capacitor connected between said common line and oneside of said parallel resistance capacitance circuit.
 5. Theintervalometer of claim 4 wherein said delay capacitor is connectedbetween said common line and the emitter of said unijunction transistor.6. The intervalometer of claim 4 wherein said delay capacitor isconnected between said common line and the junction of said power supplywith said resistance capacitance circuit, and wherein a unidirectionaldevice is connected between said power supply and said delay capacitor,whereby in the event of temporary power supply dropout, said delaycapacitor will retain a charge sufficient to continue operation of saidoscillator.
 7. An electronically timed mechanical intervalometer forsequentially firing a group of ordnance devices, said intervalometercomprising: a plurality of banks of switches, a solenoid connected todrive said banks of switches, said solenoid having an energizing coiland a set of self-interrupting contacts therefor, a coil-energizingswitch for repetitively energizing said solenoid coil, and an oscillatorfor repetitively closing said coil-energizing switch, said oscillatorcomprising a unijunction transistor having a base one electrodeconnected to said power supply, having a base two electrode connected toa controlling terminal of said solenoid-coil-energizing switch, andhaving an emitter electrode, a main timing capacitor having one sidethereof connected to said emitter electrode of said unijunctiontransistor, a first resistor connected between one side of said powersupply and the other side of the timing capacitor, a second resistorconnected in parallel with said capacitor, and a delay capacitorconnected between the other side of said power supply and one side ofsaid main timing capacitor.
 8. The intervalometer of claim 7 whereinsaid capacitors comprise a capacitive voltage divider connected betweena junction of said first and second resistors and said other side of thepower supply, said voltage divider having a tap connected to saidemitter electrode of the unijunction transistor.
 9. The intervalometerof claim 7 wherein said delay capacitor is connected between said otherside of said timing capacitor and said other side of said power supply.10. In an intervalometer having a stepping switch connected to fire agroup of ordnance devices in sequence, said stepping switch having asolenoid and solenoid-energizing coil adapted to be energized through acoil-energizing switch from a power supply for incrementally rotatingthe switch, the improvement comprising a timing oscillator forperiodically energizing said solenoid coil at a selected repetition ratein a sequence of energizations that begins substantially instantaneouslyon application of power from said power supply, said timing oscillatorcomprising an oscillator switch having an output connected to operatesaid coil-energizing switch and having a triggering electrode connectedto be substantially isolated from steady-state levels of said powersupply and to respond to sharply rising increases thereof as occur uponturn on of the power supply, an RC timing circuit connected to becharged from said power supply and to provide a triggering signal tosaid triggering electrode upon attainment of a predetermined voltagelevel, said timing circuit connected to be discharged by actuation ofsaid oscillator switch, whereby said oscillator switch and said coilenergizing switch are actuated substantially instantaneously upon turnon of the power supply and intermittently thereafter each time saidtiming circuit attains said predetermined charge.
 11. In anintervalometer having a stepping switch connected to fire a group oFordnance devices in sequence, said stepping switch having asolenoid-energizing coil adapted to be energized through acoil-energizing switch, the improvement comprising a timing oscillatorfor periodically initiating energization of the solenoid coil at aselected repetition rate in a sequence of energizations that beginssubstantially instantaneously upon application of power from said powersupply, said oscillator comprising an oscillator switch having an outputelectrode connected to actuate said coil-energizing switch, and havingan input electrode arranged to trigger said oscillator switch uponattainment of a predetermined signal level at said input electrode, acapacitor connected in series circuit with said power supply and saidinput and output electrodes of said oscillator switch, whereby a suddenincrease in voltage of said power supply, as occurs upon turn on of thecircuit, is transmitted to said input electrode of the oscillator switchsubstantially instantaneously, and said capacitor is discharged bycurrent conducted from said input to said output electrodes of saidoscillator switch, and a charging circuit connected to charge thecapacitor from said power supply when said oscillator switch isnonconducting, whereby after the first actuation of the oscillatorswitch that occurs substantially instantaneously upon turn on of thepower supply, the oscillator switch will be operated periodically uponrecharging of the capacitor through said charging circuit.
 12. Theintervalometer of claim 11 including a second capacitor connected withsaid first-mentioned capacitor to form a capacitive voltage dividerconnected across said power supply and having a tap thereof connected tosaid input electrode of said oscillator-switching device.
 13. Theintervalometer of claim 11 including a second capacitor connected tomomentarily delay the sharp rise of voltage transmitted through saidfirst capacitor to said input electrode of the oscillator-switchingdevice upon turn on of the power supply, said second capacitor beingconnected between said input electrode of the oscillator-switchingdevice and ground.
 14. The intervalometer of claim 11 including a secondcapacitor connected to momentarily delay the sharp rise of voltagetransmitted through said first capacitor to said input electrode of theoscillator-switching device upon turn on of the power supply, saidsecond capacitor being connected between ground and said power supply,and a unidirectional conducting device series connected between saidsecond capacitor and said power supply to enable said second capacitorto store and retain a charge sufficient to power said oscillator in theevent of temporary dropout of said power supply.
 15. An intervalometerfor providing electrical firing signals at a selected frequency and in aselected sequence that starts substantially instantaneously upon afiring command for firing a group of ordnance devices, saidintervalometer comprising: a power supply and a firing switch connectedthereto, a stepping switch including a driving coil connected to beenergized by said power supply through said firing switch, aninterrupter switch in circuit with said coil between said firing switchand the coil for momentarily disconnecting the coil from the powersupply after the coil has been energized and upon substantial completionof one step of the stepping switch, an externally actuated coilenergizing switch connected in series circuit with said coil and powersupply to initate energization of the coil upon actuation of saidcoil-energizing switch and to maintain such energization until saidinterrupter switch is operated to disconnect said coil from said powersupply and firing switch, whereby the coil is energized by eachactuation of said coil-energizing switch and is self deenergized byoperation of said interrupter switch.
 16. The intervalometer of claim 15including an oscillator connected to be energized from said power supplyand fire control switch for providing a cyclically repetitive outputtrigger at the beginning of each cycle of the oscillator and forproviding a first output trigger signal substantially immediately uponapplication of power to the oscillator from the power supply and firecontrol switch, the output of said oscillator being connected to actuatesaid coil-energizing switch into conductive condition to thereuponinitiate energization of said solenoid coil.
 17. The intervalometer ofclaim 16 wherein said oscillator has a natural frequency considerablyless than the natural frequency of said stepping switch whereby aftereach energization of the stepping switch coil that occurs upon actuationof the coil energizing switch, the coil is self deenergized by operationof the interrupter switch and remains deenergized until thecoil-energizing switch is once again actuated by the output of saidoscillator.
 18. The intervalometer of claim 17 wherein saidcoil-energizing switch comprises a silicon-controlled rectifier havingan anode and cathode connected in series circuit with said solenoid coiland having a control electrode, and wherein said oscillator comprises aunijunction transistor relaxation oscillator that includes a base twoelectrode connected to the control electrode of the silicon-controlledrectifier.
 19. The intervalometer of claim 17 wherein said coilenergizing switch comprises a silicon-controlled rectifier having ananode and cathode in series circuit with the solenoid coil and having acontrol electrode, and wherein said oscillator comprises a unijunctiontransistor having a base one electrode connected to said power supplyand fire control switch, and having a base two electrode connected tosaid control electrode of the silicon-controlled rectifier and having anemitter electrode, a capacitor connected between said emitter electrodeand the power supply and firing switch, and a charging resistorconnected across the capacitor.
 20. The intervalometer of claim 19including a second capacitor connected between said power supply andground, and a second resistor series connected between said secondcapacitor and said power supply and firing switch, whereby the sharprise in voltage occurring upon closing of the firing switch is appliedto said emitter electrode substantially instantaneously across saidfirst capacitor, but is momentarily delayed in application to theemitter by means of the delaying action of the second resistor andsecond capacitor so as to prevent operation of said unijunctiontransistor for a short period in the order of the time required forswitch bounce.
 21. The intervalometer of claim 20 including avoltage-regulating transistor connected between said s second resistorand said firing switch, said voltage-regulating transistor having a baseelectrode, a zener diode connected to said base electrode forestablishing a substantially constant voltage level at such baseelectrode, and a third resistor connected across the collector and baseelectrodes of the voltage-regulating transistor.
 22. The intervalometerof claim 20 including a spurious voltage protection circuit connectedbetween the said oscillator and said power supply and firing switch,said protection circuit comprising a protection transistor havingemitter and collector electrodes connected between said second resistorand said firing switch and having a base electrode, and a zener diodeconnected between the base electrode and ground, whereby said protectiontransistor will not conduct until a signal at one of said collector andemitter electrodes rises above a predetermined potential levelestablished by said zener diode and the voltage drop across saidprotection transistor.